The National Cancer Institute's Cancer Prevention Research Program.

The National Cancer Institute (NCI) develops and supports a broad range of research relevant to screening for preneoplastic events and biological effects of carcinogen exposure. In cancer screening and detection, NCI supports studies on development of new methods for detecting cancer and/or preneoplastic states, systematic testing of new screening methods, and wider application of established methods. Recently, NCI developed clinical trials in chemoprevention and dietary intervention. These studies focus on populations identified by markers of exposure or markers of increased risk, and have as their end point reduction in cancer incidence.

The effects on rat pups when nitrofen (4-(2,4-dichlorophenoxy)nitrobenzene) was applied dermally to the dam during organogenesis.

Nitrofen (4-(2,4-dichlorophenoxy)nitrobenzene; TOK herbicide) was administered dermally as an aqueous dilution of an emulsifiable concentrate on Day 6-15 of gestation to pregnant Sprague-Dawley rats at dose levels of 0, 0.3, 0.6, 1.2 and 12.0 mg/kg/day. No maternal toxicity occurred. At 12 mg/kg neonatal survival was reduced and the animals that died had a high incidence of diaphragmatic hernias. Survivors showed increased incidences of diaphragmatic hernias and of missing or reduced Harderian glands, chromodarcryorrhea (a clear red exudate around the eyes), and a high frequency of slight to severe dilation of the renal pelvis. Thyroid and Harderian gland weights were significantly depressed in Day 42 survivors of both sexes at 12.0 mg/kg; liver and lung weights were decreased, and renal weight was increased in the females. At 12.0 mg/kg thyroid weights of males and females were significantly depressed at 146 days postnatal. The incidence of dilated kidneys was increased at 0.3 mg/kg and higher. No effect was observed at any dose level on time to eye opening, time to vaginal opening, mitotic index of the liver, or T3 levels in the dams or the offspring, and no gross behavioral effects were recorded. The no observable effect level was estimated to be 0.28 mg/kg in males and 0.17 mg/kg in females using a mathematical extrapolation.

Distribution and metabolism of the teratogen nitrofen (2,4-dichloro-4'-nitro diphenyl ether) in pregnant rats.

Oral exposure of pregnant Long-Evans rats on day 11 of gestation to the teratogen, nitrofen (2,4-dichloro-4'-nitro diphenyl ether), which was uniformly labeled with 14C in the nitrophenyl ring, resulted in the accumulation of radioactivity in maternal fat with lesser amounts found in liver, kidney, other tissues, and in the embryonic compartment. The peak concentration of radioactivity occurred 7-9 h after dosing and the half-life of the label in maternal blood was approximately 8 days. In the embryonic compartment, radioactivity was first detected at 2 h after dosing, peaked at 4-6 h, and declined to half of that initially seen by 24 h. High performance liquid chromatography of embryo-placental extracts revealed 4 metabolites in addition to the parent compound: 4'-amino and 4'-acetylamino derivatives plus 2 hydroxylated derivatives. A similar metabolic profile was observed in maternal blood and liver. In another experiment, purified 4'-amino metabolite was found to have no adverse effect on neonatal survival when administered orally on day 11 of gestation at doses up to 215 mg/kg. These results suggest that the teratogenicity of nitrofen cannot be readily explained by preferential distribution of the compound in the embryo or by a unique profile of stable, extractable metabolites in the embryonic compartment.

The heart and diaphragm: target organs in the neonatal death induced by nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether).

This paper examines the effects of in utero exposure to 2,4-dichlorophenyl-p-nitrophenyl ether (nitrofen) on the viability of neonatal Long-Evans rats. Oral administration of this herbicide on days 8-18 of gestation reduced neonatal survival and birth weight. Day 11 of gestation was the most sensitive day for induction of neonatal mortality; 116 mg/kg to the dam on this day was the LD50 for the neonate. An increased incidence of hydronephrosis was observed in 35-day survivors. This increase was dose-related in animals exposed on day 11 of gestation. Fetuses exposed on day 11 and examined at term had reduced weights, delayed skeletal ossification, and an increased frequency of hydronephrosis and diaphragmatic hernias. While nitrofen did cause a high incidence of hydronephrosis, BUN or creatinine levels in 4-h neonates were not elevated. Detailed examination of the hearts of term fetuses revealed cardiac malformations classified as ventricular septal defect, double outlet right ventricle, and transposition of the great vessels. We conclude from these studies that the heart and the diaphragm are the target organs in nitrofen-induced neonatal death.

Reproducibility of serum haptoglobin profiles in mice with transplanted tumors.

To determine whether the elevation of serum haptoglobin (Hp) elicited by many tumors is associated with properties of the tumor, Hp levels were determined during successive passages of two transplantable fibrosarcomas and two leukemia lines in syngeneic mice. Characteristic and unique profiles were elicited by each of the four tumors and were reproducible in each of three successive transplant generations. The Hp profiles elicited by EL4 leukemia cells were similar in allogeneic and syngeneic mice, except that the Hp maxima were greater in the allogeneic mice. Preimmunization with EL4 cells or pretreatment with immune serum or spleen cells obliterated the Hp response normally elicited by EL4 cells in allogeneic mice. These results suggest that the Hp response elicited by a tumor is associated with transmissible characteristics of the tumor.

Effects of poly-L-lysine on infectious viral nucleic acid.

Infectious ribonucleic acids (IRNA) of Venezuelan equine encephalitis and Eastern equine encephalitis viruses were observed to form noninfectious complexes with a basic polyamino acid, poly-l-lysine. Original infectivity was recovered from the complexes by digestion of the polylysine with Pronase, and partial recovery was effected by treatment with sodium dodecyl sulfate. Infectivity could not be recovered from the complexes containing polylysine of 100,000 molecular weight by changes in ionic strength, pH, or by treatment with phenol, deoxycholate, or digitonin. Masking of infectivity by polylysine was demonstrated in vivo as well as by plaque assay in tissue culture. Poly-l-lysine preparations of high molecular weight (44,000 to 100,000) were more effective than low molecular weight (3,000) materials in masking infectivity of IRNA. When complexes, in which infectivity had been masked by low molecular weight polylysine, were suspended in 1 m NaCl, some infectivity was recovered. Complexes of polylysine-IRNA differed from control IRNA alone in (i) resistance to inactivation by ribonuclease, (ii) sedimentation patterns in sucrose gradient centrifugation, and (iii) stability of recoverable infectivity during different physical treatments.